Runtime-dependent switching off of the echo compensation in packet networks

ABSTRACT

The invention relates to the switching off of echo compensations as a function of the useful data transmission time for a packet network. On changes to a packet network connection, for example with relation to a diversion or forwarding of speech connections, the useful data transmission time for the changed packet network connection is determined. Where the determined useful data transmission time falls below the threshold value, the switching off of the echo compensation is carried out. The invention permits the dynamic switching off of echo compensators which are no longer required, due to a reduced useful data transmission time.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/DE03/01948, filed Jun. 11, 2003 and claims the benefit thereof.The International Application claims the benefits of German applicationNo. 10229680.4 filed Jul. 2, 2002, both of the applications areincorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a method and a gateway for switching off anecho compensation for a useful data connection in a packet network whileshortening the packet delay time.

BACKGROUND OF INVENTION

In switching technology, methods for the echo compensation play animportant role for high-quality speech transmission.

A distinction is typically made in telephony between the following threefactors which reduce the quality during speech transmission: delay time,signal distortions and echo. The effect of echo, i.e. the reflection ofspeech signals depends on the signal delay time. In general, an echowith a limited time interval, e.g. 25 to 30 ms, hardly impairs thequality of a telephone call. A specific form of echo with a delay ofapproximately 28 ms, namely local echo, even has the desired effect thatthe speaker, when speaking, hears his own voice from the ear piece.However, in the case of a longer signal delay time, the result is agreater adverse effect on the quality of the telephone call because ofecho effects, which is why echo is suppressed with echo compensationmethods.

Echo compensation is a method established for time division multiplexingnetworks in “classic” telephony. Transmitting speech over packetnetworks such as IP (Internet Protocol) networks, results in a changedsituation compared to time division multiplex networks:

Packets are routed in the packet network. They are routed on the basisof destination addresses. When routing of packets is changed (e.g.rerouting as part of call diversion), the destination address is usuallyreplaced in the packet headers by the address of the new destination.Packets are routed to the new destination independent of the originaldestination. As a result, the transmission time to the new destinationcan be shorter or longer than that for the original destination.Transmission to the new destination can require a switching on or aswitching off of the echo compensation.

Modern packet networks allow “virtual trunking”, i.e. the separaterouting and transmission of signaling messages and useful data. Measuresfor echo compensations must take this more complex architecture intoaccount. The methods specific to the packet network for setting up andcontrolling the connection, e.g. by specifying the address in the packetheader, lead to new methodical requirements compared to the timedivision multiplex networks.

SUMMARY OF INVENTION

The object of the invention is the delay time-dependent switching off ofthe echo compensation in packet networks.

The invention relates to the situation in which an echo compensationprovided for a connection must be switched off in a packet networkbecause, as part of a change in the packet delay time or thetransmission time of useful data, echo compensation is no longerrequired. According to the invention, a threshold value is used for theuseful data transmission time or the delay time of the useful data thatrepresents a lower limit for switching off the echo compensation. Whenthe useful data connection or the packet delay time are changed, e.g.within the framework of call forwarding, the new useful datatransmission time is determined for a changed packet transmission link.If echo compensation is switched on, a subsequent test is carried out todetermine whether or not the specific useful data transmission time ofthe changed useful data connection falls below the threshold value forswitching off the echo compensation and, in falling below the thresholdvalue, switches off the echo compensation.

Forwarding or diverting a connection in the packet network can result ina shorter transmission time for useful data because useful data isusually not routed via the original destination to the new destinationwithin the context of the diversion. Instead, address information aboutthe new destination is usually used for the routing which replaces theaddress information of the old destination. The packet delay time or theroute regarding routing to the new address can be shorter than in thecase of the original connection. The specification in the invention of alimit, e.g. 32 ms for switching off the echo compensation, supplies acriterion for providing the echo compensation. If the limit or thethreshold value is undershot, the echo compensation should be switchedoff. Such a switching off is recommended, for example, in the standardG. 131 ITU-T “Control of Talker Echo” in section 5.2.1.1, Rule 7:“Connections that do not require Echo Control Devices should not befitted with them, because they increase the fault rate and are anadditional maintenance burden”. A criterion for the decision of therecommended switching off of the echo compensation in the case of shorttransmission times is given according to the invention by determiningthe useful data transmission time for the changed circumstances or theconnection and comparing the new useful data transmission time to thethreshold value. Where the new useful data transmission time falls belowthe threshold value, the echo compensation is switched off. An existingecho compensation can thus be suppressed dynamically and as required insuch a way.

In many modern packet-based networks, signaling messages and useful dataare transmitted separately. The connection control is then handled bycontrol devices such as media gateway controllers and in relation to IN(Intelligent Network) concepts these control devices are referred to asService Nodes (abbreviated SN). The useful data is transmitted by meansof gateways, e.g. media gateways, access gateways or residentialgateways which transports the useful data packets or useful data flowsaccording to address information. In this situation, a distinction ismade between three groups of protocols used. On the signaling level,control or signaling information is exchanged by means of protocols suchas the BICC protocol (BICC: Bearer Independent Call Control), an adaptedISUP protocol (ISUP: ISDN User Part) or the SIP protocol (SIP: SessionInitiation Protocol). On the level of useful data transmission,application-specific protocols such as the RTP protocol defined in theRFC (Request For Comments) 1889 “Transport protocol for real timeapplication” which was especially designed for speech and videotransmission are used. Finally, protocols for communication betweenthese two levels or the device elements on the signaling level and thedevice elements on the useful data level are required. For this, theMGCP (Media Gateway Control Protocol) is, for example, used which isdefined in RFC2705 or the protocol defined in ITU-T H.248. At lowerlevels overlaps with regard to the protocol stacks used can occur forthe three groups of protocols, for example, the IP protocol on thetransmission level and the UDP or the TCP protocol on the transportlevel. As a result, in an embodiment of the invention for a separatetransmission of the signaling and the useful data in packet networks, acontrol device and a gateway are used for the method according to theinvention. In this embodiment, the control device and the gateway canalso be implemented in a physical device by means of integrated logicalfunctions. In order to send the threshold value from the control deviceto the gateway, the MGCP protocol can, for example, be used. To thisend, the MGCP protocol is expanded in an embodiment of the invention: Anew event is provided in the RCP package of the MGC protocol. This eventcan be defined as “Propagation Delay Decreased” and includes thenumerical value of the duration as a parameter for the threshold value.This expansion then takes the following form in accordance with thenotation of RFC2705: Symbol Definition R S Duration PDD(###) Propagationdelay X decreased

In this case, “###” symbolizes a numerical value for the delay or theuseful data transmission time, for example, in ms. The modified RTPpackage can, as part of a notification request or an encapsulatednotification request, be sent from the control device to the gateway,for example, in the course of a create connection message. On changingor diverting the useful data connection, for example, in the course of abearer redirection procedure which is described in the ITU-T Q.1902.6standard specification, the gateway determines the useful datatransmission time of the changed useful data connection. The useful datatransmission time can be determined at regular intervals, e.g. in theform of checking a network congestion which manifests itself in acorresponding increase in the transmission times. Alternatively, usefuldata transmission time measurements are triggered by changes in theuseful data connection. For example, as part of the bearer redirectionprocedure for diverting the useful data stream transferred signalingmessages will trigger the measurement of the useful data transmissiontime.

The useful data transmission time can, for example, be established bydetermining the round trip for packets described in the RFC (Request ForComments) 1889 section 6.3.1. Half of the round trip for packetsdetermined with this procedure represents an estimation for the usefuldata transmission time of the connection searched for in which case thisinformation is combined with the jitter buffer which describes thevariance in the arrival of packets. After the useful data transmissiontime has been determined, it is compared with the threshold value andreported to the control device should the determined useful datatransmission time fall below the threshold value. Based on this message,the control device switches off the echo compensation.

For the described sequences in the gateway, a procedure for determininguseful data transmission times can, for example, be implemented in thisgateway by means of a method for determining the round trip described inthe RFC1889. In addition, program structures are necessary which permita comparison of useful data transmission times determined with thethreshold value given by the control device. The echo compensation canalso be switched off via the gateway if the echo compensation is in thegateway's area of responsibility. When the MGC protocol is used, thisswitching off of the gateway can also be carried out by using the MDCXinstruction (MDCX: Modify Connection) which is transmitted from thecontrol device to the gateway.

Another situation results if the echo compensation is not in the area ofresponsibility of the control device or of a gateway controlled by thecontrol device. In this case, the switching off request can be signaledto another control device by using the enhanced echo control procedurewhich is described in section 2.7.2 of the ITU-T standard Q.764. Thisfunctions by means of sending an NRM (Network Resource Management)message by means of the protocol used on the control level, saidprotocol being, for example, the ISUP or the BICC. According to table 46of the ITU-T standard Q.763 “signaling system No. 7—ISDN user partformats and codes”, the NRM message can contain an “echo controlinformation” parameter, i.e. be used for transporting controlinformation for the echo compensation.

The addressee of the NRM message is a control device that has accessdirectly or indirectly (i.e. via a gateway) to the echo compensation tobe switched off. On receipt of the NRM message, this control deviceactivates the desired switching off process.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments of the invention are shown and explained in thefollowing by way of drawings. They are as follows:

FIG. 1A system for a connection of PSTN users routed via a packetnetwork separately transmitting the signaling messages and the usefuldata

FIG. 2 Diversion of the A-side useful data flow to an IVR server (IVR:Interactive Voice Response)

DETAILED DESCRIPTION OF INVENTION

In this case, the same reference symbols designate the same elements.

FIG. 1 shows a typical speech connection of two PSTN users TLN-A andTLN-B routed via a packet network IPNET. In this case the useful dataand signaling messages are transmitted separately in accordance with theSS7 system (SS7: Signaling System No. 7). The end users TLN-A and TLN-Bare in each case connected to the PSTN (Public Switched TelephoneNetwork) network via local trunk exchanges LE that are close to theuser. Via one or more transit exchanges TX of the PSTN network, usefuldata can be transmitted to network access devices or to gateways MG-A orMG-B (MG: Media Gateway). Useful data transmitted from the A-user TLN-Ato the B-user TLN-B is adapted in the network access devices MG-A orMG-B for speech transmission via the packet network IPNET. For a packetnetwork operating on the basis of the IP (Internet Protocol) protocol,the transmission of speech is referred to as voice-over-IP, abbreviatedas VoIP. As a result, signaling for setting up the connection betweenthe two users TLN-A and TLN-B is handled separately by the useful datatransmission. Signaling messages transmitted from the PSTN networkwithin the context of connection control are sent to the control deviceor the media gateway controller MGC-A by using the ISUP (ISDN UserPart). By sending control messages to the network access device MG-Ausing the MGCP protocol, the control device MGC-A activates the controlof the transmission of useful data via the packet network IPNET. In thecase of a system which is embodied according to an IN (IntelligentNetwork) architecture, the control devices MGC-A or MGC-B are referredto as service nodes (abbreviated SN). For the connection setup orconnection control between the end users TLN-A and TLN-B, signalingmessages are exchanged between the control device MGC-A and the controldevice MGC-B which control the B-side network access device MG-B. Thisexchange of messages is carried out, for example, by using the BICC CS2(Barer Independent Call Control—Capability Set No. 2) protocol.Therefore, signaling messages can then be forwarded from the B-sidecontrol device MGC-B to the B-side PSTN network by using the ISUPprotocol.

FIG. 2 shows the system from FIG. 1, with an IVR (Interactive VoiceResponse) server IVR-S being shown as the additional device element.This IVR server is controlled by the control device MGC-A through theMGC protocol. IVR servers serve to provide speech-associated servicefeatures such as creating announcement texts or providing automateddialog sequences. For example, as part of a connection setup request ofthe user TLN-A with the B-user TLN-B, the non-accessibility of theB-user TLN-B is established and an announcement function provided by theIVR server IVR-S is activated which informs the A-user TLN-A about thenon-accessibility of the B-user. Therefore, in the case of incorrectlyentered call number information, the IVR server IVR-S, for example,outputs for the A-user TLN-A, the text “no connection under thisnumber”. In order to access the IVR resources that are provided by theIVR server IVR-S, the useful data connection to the IVR server IVR-Smust be diverted. For this, the bearer redirection procedure which isdescribed in the ITU-Q.1902.6 standard specification is, for example,available. As part of this procedure, the useful data connection betweenthe network access devices MG-A and MG-B is replaced by the useful dataconnection between the network access device MG-A and the IVR serverIVR-S. Changing this path of the useful data brings about a change inthe transmission link resulting in a new situation regarding thenecessity for an echo compensation. For example, an echo compensationwas needed for the useful data connection between the MG-A and the MG-B(shown with a dotted line in FIG. 2) which is not relevant to the usefuldata connection between the access device MG-A and the IVR server IVR-S.According to the invention, this is expressed by the fact that theuseful data transmission time falls below a threshold value. Such auseful data diversion that requires a splitting off of the echocompensation is detected in the network access device MG-A and reportedto the control device MGC-A. For detecting a change in the useful dataconnection, the network access device MG-A is programmed or configuredby the control device MGC-A as part of the connection setup or isprogrammed or configured during the connection. On using the MGCPprotocol according to the RFC2705 standard, procedures for theinstruction to the network access device MGC-A described therein can beused. For example, the instruction “notification request” is used. Thisinstruction can be used to activate gateways for sending information(notification) about the occurrence of specific events to the authorizedgateway controller. The notification request contains a list ofinstructions (in the “Requested Events” standard) to be implemented by amedia gateway. Within the framework of the protocol, so-called eventpackages are defined which specify lists of events and actions that canbe detected or carried out. Such a package is the so-called RTP (RealTime Protocol) package which is used for the control or to control RTPflows. Therefore, in this package, a new requested event is introducedwith the name ‘propagation delay decreased’ which includes as parameterthe threshold value for switching off the echo suppressors. As a result,the RTP package can be sent as part of the notification request to thenetwork access device MG-A. Therefore, on receiving the notificationrequest, the network access device MG-A detects a change in the networkdata transmission and sends a signal to the control device MGC-A thatthe data transmission is falling below the threshold value. Thenotification request can also be sent from the control device MGC-A tothe network access device MG-A as an optional element of the createconnection instruction, typically in the form of an encapsulatednotification request as part of the connection setup. Alternatively, thenotification request—typically if a connection has already been setup—is sent as an independent command or independent instruction to thenetwork access device MGC-A. If a create connection instruction is used,the connection setup introduced by this instruction is at the same timecarried out with the measures required by the notification request fordetecting a change in the useful data transmission.

Changes in the useful data transmission as, for example, shown in FIG. 1measure the delay time of the new useful data connection arising (inFIG. 2 between the network access device MG-A and the IVR server IVR-Sinstead of the connection drawn in dotted lines between the networkaccess devices MG-A and MG-B). The transmission time is, for example,measured by using the round trip delay measurement described in theRFC1889, section 6.3.1 (referred to as ‘round trip delay’ in thestandard). In this case, packets are sent to the new destination or thenew end point and then back again. The duration for the round trip ofthe packet can be determined from the time stamp or the time informationentered for the new destination. In order to reduce the influence ofscattering in the transmission time of packets, the jitter buffer whichdescribes the variance in the arrival of packets is usually also used.The value thus received for the round trip delay is divided by two andcompared with the threshold value for switching off the echocompensation. If the delay time of the packets complies with thecriterion for switching off the echo compensation, the network accessdevice MG-A informs the control device MGC-A. A switching off of echocompensations in the case of the network access device MG-A can be usedby the MGCP instruction Modify connection (MDCX) which takes the localconnection options as the parameter. The local connection optioncontains a field “Usage of Echo Cancellation” which by using the values“on”, “and” or “off” makes possible the switching off or switching on ofthe echo compensation.

According to the invention it is also possible to switch off echocompensators which do not lie within the range of the media gatewaywhich is responsible for detecting the useful data transmission time. Ina variation on the above-mentioned embodiment, the useful datatransmission time is measured by the B-side media gateway MG-B. Forexample, by means of the B-side media gateway it is possible todetermine that on the basis of network fluctuations the packets sent bythe A-side media gateway MG-A arrive more quickly than before and thatthe echo compensator must be switched off in the case of the A-sidemedia gateway. Contrary to the case described in FIG. 2, if the usefuldata delay time is detected in the B-side media gateway MG-B, the echocompensation can no longer be switched off directly by means of controlcommands transmitted by the control device MGC-A. Instead, the controldevice MGC-B signals to the A-side control device MGC-A that the echocompensation must be switched off. The echo compensation can then againbe undertaken by the control device MGC-A to the media gateway MG-A bymeans of MGCP commands or instructions. In order to signal the exceedingof the threshold value or the necessity for switching off the echocompensation by the network access device or the control device MGC-B tothe control device MGC-A, procedures can be used that are given in thestandard code Q.764 “Signaling System No. 7—ISDN User Part SignalingProcedures” in section 2.7.2 “Enhanced Echo Control SignalingProcedures”. By means of an NRM (Network Resource Management) messagethat is generated, for example, on receiving an ECRF (Echo ControlRequest Forward) event, the control device MGC-A triggers the switchingoff of the echo compensation, i.e. the control device MGC-A is activatedto send an MGCP instruction to the media gateway MG-A for switching offthe echo compensation.

1-9. (canceled)
 10. A method for switching off an echo compensation fora data connection in a packet network when a packet delay time isreduced, comprising: establishing a threshold value of a datatransmission time that represents a lower limit for switching off theecho compensation; changing the data connection triggers changing thedata transmission time of the changed data connection; determining ifthe data transmission time of the changed data connection dropped belowthe threshold value when the echo compensation is switched on; switchingoff the echo compensation via a control device and a gateway, andsending the threshold value from the control device to the gateway whenthe determined data transmission time falls below the threshold value,determining the data transmission time of the changed data connectionwhen the gateway changes the data connection; checking by the gateway ifthe data transmission time of the changed data connection falls belowthe threshold value when the echo compensation is switched on; informingthe control device from the gateway that the data transmission time fellbelow the threshold value; and switching off the echo compensation onreceiving information that the data transmission fell below thethreshold value.
 11. The method according to claim 10, wherein from thecontrol device to the gateway, as part of a transfer of the thresholdvalue via a notification request instruction of a media gateway controlprotocol, the gateway is made to inform the control device when there isa change in the data connection which causes it to fall below thethreshold value.
 12. The method according to claim 10, wherein thethreshold value is sent via an event in a real time protocol package ofthe media gateway control protocol.
 13. The method according to claim10, wherein the data transmission time is determined by using a roundtrip of a message.
 14. The method according to claim 10, wherein whenthe data transmission falls below the threshold value the echocompensation is switched off by the control device by sending a MDCXmedia gateway control protocol message to the gateway.
 15. The methodaccording to claim 10, further comprising: sending a network resourcemanagement message for switching off the echo compensation to a firstcontrol entity when the echo compensation is switched off in a servicearea of a second control entity; receiving the network resourcemanagement message by the second control entity; and switching off theecho compensation in the second control entity.
 16. The method accordingto claim 10, further comprising: sending a network resource managementmessage for switching off the echo compensation to a control entity whenthe echo compensation is switched off in the service area of the controlentity; and switching off an echo compensation by the control entity.17. The method according claim 10, wherein the packet network is aninternet protocol network.
 18. The method according claim 10, whereinthe packet network is an asynchronous transfer mode network.
 19. Themethod according claim 10, wherein the data transmission time isdetermined at predefined intervals.
 20. A communication system in apacket network for switching off an echo compensation for a connectionin the packet network, comprising: a gateway operatively connected tothe packet network, the gateway adapted to monitor a transmission timeof a packet for the connection when the echo compensation is on; and acontrol device operatively connected to the gateway that is informed bythe gateway when the transmission time has fallen below a thresholdvalue, the control device informing the gateway when the echocompensation is to be switched off.
 21. The system according to claim20, wherein the transmission time is determined at predefined intervals.22. The system according to claim 20, wherein determining thetransmission time is triggered by a connection change.
 23. The systemaccording to claim 20, wherein the gateway switches off the echocompensation.
 24. The system according to claim 20, wherein thetransmission time is determined by using a round trip of a message. 25.The system according claim 20, wherein the packet network is an internetprotocol network.
 26. The system according claim 20, wherein the packetnetwork is an asynchronous transfer mode network.
 27. A communicationsystem in a packet network for switching off an echo compensation for aconnection in the packet network, comprising: a gateway operativelyconnected to the packet network, the gateway adapted to monitor atransmission time of a packet for the connection when the echocompensation is on and turning off the echo compensation when thetransmission time falls below a threshold value; and a control deviceoperatively connected to the gateway.
 28. The system according to claim27, wherein the transmission time is determined at predefined intervals.29. The system according to claim 27, wherein determining thetransmission time is triggered by a connection change.